It was one of the great missed connections of physics. In 1965 a particle theorist derived a formula for the collision of elementary particles. Twenty years later two gravitation theorists, using completely different techniques, derived a formula for the collision of stars or black holes. And they were the same formula. The only difference was that the first used “p” to denote momentum and the second used “P”. Harvard physicist Andy Strominger jokes that “a 6-year-old could look at those two papers” and spot the similarity. But evidently no 6-year-old did, so their resemblance went unnoticed until Strominger realized it in 2014.
What the formulas have in common is that they concern how gravity and other forces act on large scales. Strominger and his colleagues have been investigating how they may offer a new and unusual path to unifying the laws of physics. The large-scale behavior of forces turns out to hold as many surprises as the small-scale behavior that physicists traditionally focus on. The approach has also opened a fresh line of attack on a notorious paradox about the fate of information about objects that are swallowed by black holes, first identified by Stephen Hawking in the 1970s. “Andy’s work is very important and will eventually have a large impact on many areas of physics,” says Éanna Flanagan of Cornell University.